1. Field of the Invention
The present invention relates to an engine control system and method and particularly to an engine control system and method in which fuel injection, air induction and exhaust gas recirculation are integrally controlled corresponding to an operator's accelerator operation.
2. Prior Arts
Modern automobile internal combustion engines are required to meet various requirements such as emissions, fuel economy, driveability, performance and the like. One solution to satisfy these requirements is a stratified charge combustion engine. In conventional engines, since fuel injection quantity is determined from the amount of air passing through the throttle valve, the air-fuel ratio can not be changed largely. On the other hand, the stratified charge engine is required to be operated within a wide range of air-fuel ratio. When the air-fuel ratio changes abruptly, the change of torque would exceed an allowable limit of driveability unless the amount of injected fuel is determined in accordance with changing torque.
Recently, several techniques have been proposed in which the required amount of fuel and air is determined on the basis of engine torque. For example, Japanese Patent Application Laid-open No. Toku-Kai-Hei 1-313636 discloses a technique wherein first, a target engine torque is determined based on the accelerator depressing amount and the engine speed, then the fuel injection amount is controlled according to this target engine torque and at the same time the intake air amount is controlled by electronically adjusting the opening angle of the throttle valve through an actuator.
In transient operating conditions of the engine, however, it is difficult to supply a proper amount of air, because there is a deviation due to a time lag needed for charging air in the intake manifold and the collector chamber having a certain volume or due to a time lag of operation in actuating devices, between the required air amount corresponding to the target torque and the actual air amount sucked into the cylinder. Due to this, there is a difficulty in supplying appropriate amounts of air and fuel.
To solve the problem, Japanese Patent Application Laid-open No. Toku-Kai-Hei 3-185248 discloses a technique in which compensation is made to a phase lag corresponding to time lag of intake air and actuating devises with respect to the target torque or the fuel injection amount itself so as to prevent an excessive or short fuel supply to cylinders.
However, since the aforementioned throttle valve control according to the prior arts are performed based on an open-loop control strategy but not a feedback control strategy, air flow deviations or air flow changes produced from variations between throttle valves, changes of the opening area of the throttle valve due to temperature change or stains on throttle valves can not be deleted.
Further, in case of an engine employing an EGR valve for reducing emissions, there is a delay of response of the EGR valve caused by a time lag needed for charging the EGR gas into the collector chamber and a time lag of operation of the EGR valve itself. It can be considered that this delay of response can be compensated by fuel injection timing or ignition timing, however it is difficult to determine under the transient condition the fuel injection timing and the ignition timing and further the target air-fuel ratio and the EGR ratio because of the difference between the response characteristic of the throttle valve and that of the EGR valve.